Quantity and topography of frog's retinal ganglion cells

blswn Rrs. Vol. 16. pp 929 10 934. Pergamon Press 1976. Pnntcd in Great Btitam.

QUANTITY AND TOPOGRAPHY OF FROG’S RETINAL GANGLION CELLS A. V. KALININA Department of Biocybernetics and Bionics, Research Institute for Applied Mathematics and Cybernetics. Lobachevsky State University. Gorky, U.S.S.R. (Receiced 21 August 1975; in revisedform 18 December 1975) Abstract-Using Rana ridibunda total retinal preparations impregnated with silver. the ganglion cells in central, middle and peripheral retinal zones are counted with the help of a calibrated eyepiece graticule. The percentage of each of the five neuron types (Kalinina, 1974) is found as well as the regularity of their distribution over the retinal zones. The digital data are processed statistically. By calculations the total quantity of the ganglion cells is evaluated as well as the sums of dendrite field areas for the different neuron types. The character of distribution of the different type neuron dendrite fields over the retinal surface is described.

The possible functional significance of the established structural properties of ganglion layer cells is discussed.

To establish the organizational principles of the retina of vertebrates one needs data on structurally and functionally heterogeneous ganglion cells’ number and distribution over the retinal surface. Quantitative investigations about the contents of various types of neurons, and in particular of ganglion cells, in the retina of vertebrates are comparatively uncommon (Chievitz. 1889; Lashley, 1932; Vilter, 1949; Weymouth. 1958; Oehme, 1961; Van Burren, 1963; Stone, 1965; and others). In spite of a considerable number of works devoted to the investigation of the frog’s ganglion cells structure (Cajal, 1893, 1909-1911 ; Lettvin, Maturana, McCulloch and Pitts, 1959; Lettvin, Maturana. Pitts and McCulloch. 1961; Maturana, Lettvin. Pitts and McCulloch, 1960; Kalinina, 1970, 1974; Shkolnik-Yarros. 1971, 1975; Venslauskas and Gutauskas, 1972, 1973; and others), only three of them contain any information on the number and distribution of the ganglion cells (Maturana, 1959; Jacobson, 1962; Shibkova, 1970). The aim of this investigation is to study the quantity and topography of various types of ganglion cells. NIETHODS The investigation was carried out using the retinal total preparations of both eyes of 10 frogs, Rena ridibunda Pall. The preparations were made according to the Gross-BiIshovsky-Lavrentyev-Feldmann method (Feldmann, 1939). The frogs weighed SO-IOOg. On the retinal plane three concentric zones of equal width were distinguished: central. middle and peripheral. Estimations of the ganglion cells’ density as well as of the cells’ percentage were made for each of the zones. The ganglion cells were counted

’ Apart from neurons in the ganglion cell layer the author distinguishes three types of glial elements: astrocyte glia. oligodendrogIiocytes and microgliocytes. Besides, among neurons of all types as well as among cells of a satellite glia there occur binuclear cells and cells with an incomplete predivision-like narrowing of nucleus (Kalinina 1969, 1974a). However. these cellular elements, occurring in the ganglion cell layer rather rarely. were not a subject of this investigation.

on a microscope MBI-6 with magnification x 1000 using an eyepiece graticule with area of 100 x IOOpm’; ceils crossed by the left and upper sides of the graticule’s square were taken into account and those crossed by the lower and right ones were not. Counting was carried out in I22 squares. The digital data were processed statistically by the Student-Fisher method (Urbakh, 1963). The retinal sites were drawn using a drawing apparatus RA-5 mounted on a microscope MBI-6, the total magnification being x ICOO. RESULTS Using R. ridibundu total retinal preparations,

five types of neurons were singled out that differed by the sizes of perikaryon and dendrite tree, by the extent and character of dendrite arborization in the internal synaptic layer, and by the shape and sizes of dendrite fields (Kalinina, 1970, 1974b). Figure 1 shows a brief characteristic of these neurons. Table 1 represents the distribution of various types of ganglion cells over the retinal zones as well as the percentage of these cells as to the total quantity.’ The genera1 density of neurons in various retinal zones was determined by means of calculations. The highest density occurs in the central retinal zone: 107.57 * 4.94 cells per 0.01 mm2. or 10,757 cells/mm’. The general density for the middle zone is about 1.5 times less and amounts to 6987 cells/mm’. The peripheral retinal zone has a comparatively low density of ganglion cells: 3735/mm’, i.e. about three times less than that of the central zone. Calculations showed the first type neurons to be the most numerous in the ganglion layer. It is their distribution over the retina1 zones that on the whole determines the general density of ganglion cells in these zones. While the first type cells’ density correlates to the general density of ganglion cells over the retina1 zones and is about three times as decreased from the central to the peripheral zone, the occurrence of the first type ceils among the cells of the other types over the zones changes insignificantly: from 96.550,/, in the central zone to 94.06% in the peripheral zone.

929

930

BeurohistologlCal ClaSsification of

gangliCXl cells

Fig. 1. The five types of neurons of the retinal ganglion layer of the lake frog. Dotted lines shou the levels of the infernal synaptic layer (schematically). Type I. The smallest neurons of the ganglion layer. The! are usual& bipolar. The dendrite. uithout ramification. reaches the middle zones of the internal plsalforal layer. Type II. Neurons of middle dimensions. From the cell body there go most often one or fwo dendrites with no more than one arborization. One of the dendrites often stretches on the level of ganglion cell bodies. the other mav reach the middle part of the internal qnaptic la?sr and sometimes its external zones. The dendiite field diameter is 59.7 e 3pm. The dendrite fields are not specifically oriented on the retinal plane. Type III. Large neurons with large cytoplasm filled with twisting neurofibrils. From the neuron body there go as a rule 2-3 dendrites that arborize 2-3 times and reach onI> the middle zone of the internal retinal layer. The dendrite fields are of comparativei> big dimensions. with a dia of 121.0 _+52pm. In relation to the dendrite tree the cell body is situated eccentricall). The dendrites ramify on the side of the cell opposite to the axon hillock. Type IV. Still larger neurons of the ganglion layer. From the perikarton most often there go 2-4 powerful dendrite branches that bifurcate 4-5 times and are distributed over various strata of the internal synaptic layer from its internal to its external boundaries. The dendrites form a considerably elongated ellipsoidal field with its-longer diameter perpendicular to rhe axons’ course. The span of the dendrites is up to 700pm. Type V. The largest retinal neurons. From the soma there usuallj go j-6 dendrites that ramify m a diffuse manner and many times in the internal synaptic layer. The dendrite field of large dimensions. the dia being up to 900ilm. is oriented similarly to that of the third type neurons.

The fourth type neurons occur more often in the periphery as compared with the central zone. Their density also increases twice from center to periphery. The percentage and density of the fourth type neurons in all the zones are significantly smaller than those of the first three types. In the central zone their number is about 950 times less that of the first type neurons, about 15 times less that of the second t,‘-pe neurons, and about 17 times less that of the third type neurons (t = 6.77; P > 0.999). In the peripheral zone these correlations are somewhat different. The fourth type neurons are almost 1ZO times less numerous here as those of the first t!pe. about 2.5 times less numerous as those of the second type (r = 2.59: P > 0.99). and five times less numerous as those of the third type (t = 5.38: P > 0.999). The percentage of the fifth type neurons in all the investigated zones is still smaller. Density parameters for them are somewhat higher in the middle zone as compared with the neighbouring ones but these

The number of the second type neurons in the central and middle retinal zones is about 60 times less that of the first type neurons. For the peripheral zone this relation is somewhat different: the number of the second type neurons here is almost 50 times less that of the first type neurons. A certain decrease of the second type neurons’ density from the retinal centre towards the periphery is not valid. At the same time the percentage of the second type neurons was observed to slightly increase in the same direction from I.54 to 1.87p0. The number of the third type neurons in the peripheral zone is I.5 times less that in the central zone. At the same time from center to periphery the percentage of the third type neurons increases from 1.76 to 3.34%. Their density is about the same as that of the second type neurons in the central zone (t = 0.3s; P > 0.2) and in the middle zone (t = 0.47; P > 0.3) and is certainly about twice as much in the periphervi (r = 2%: P > 0.98).

Table 1. Distribution of various types of ganglion cells over the retinal zones Cenmil ICI Ekrn I

II III IL L TXAl

103.56 2 133

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I.13 = 0.21 i2Y = 0.X ~0.23 " 0.08 0 165 0.07

I61 1.69 I.Si 01Y 0.33 054 0.23 1.3'

l94

100

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Quantity and topography of frog’s retinal ganglion cells differences are not certain. Nevertheless the OCCWrence of the fifth type neurons increases with certainty from 0.03‘?; in the center to 0.13:; in the middle zone and to 0.16~~ in the peripheral zone. DISCUSSION According to the data of Maturana et al. (1960) in retinal fields of dia 40-4s pm in the leopard frog, there are li-25 ganglion cell bodies. This density corresponds to the data obtained earlier by the author for the retinal peripheral zone of R. ridibunda. Unfortunately, Maturana et al. (1960) do not name the retinal zones to which their calculations are attributed. Comparison of absolute values for the ganglion cell density obtained by the author with the results of Jacobson (1963) for R. temporaria L. is not possible due to the considerable differences between the methods applied for the counting of cells (Abercrombie, 1946; Blinkov and Gleser, 1964). The highest density of the frog’s retinal ganglion cells was observed around the blind spot, i.e. somewhat temporally to the optical axis of the eye. This is consistent with the data of Jacobson (1962) for the retina of R. tempornria. The possible reasons for the formation of a smaller retinal ganglion cell density in the periphery as compared with the central zone were discussed by the author earlier (Kalin&a, 1974a). Let us attempt to estimate the general number of the retinal ganglion cells of R. ridibunda. The retinal area in the fixed and dehydrated eye cup of R. ridibunda is 163 mm2 with the internal hemisphere radius of 7 mm. The calculated total number of ganglion cells taking into account their density in each retinal zone and the area of the zone is of the order of I.OOO,OOO. If one performs the correction for the retina shrink with lixation the true retinal area will be about 243 mm2 with the eye cup radius prior to histological treatment equal to approx 9 mm (the shrinking coefficient for linear dimensions of the retina according to Stone is 19%). The total number of the ganglion cells in the retina of R. ridibunda obtained by the author exceeds twice the corresponding number for R. pipiens Shr. (Maturana, 1959). In the main the number of optic nerve fibers is determined by the number of retinal ganglion cells (Maturana, 1959). Proceeding from this let us compare the known number of optic nerve fibers of other anurans (Maturana, 1959; Nikrui. 1969; Manteyfel and Dyachkova, 1970) with that of the ganglion cells of R. ridibunda. The total number of the ganglion cells of R. ridibunda is also several times as great as the number of the optic nerve fibers of R. catesbeiana Schaw., &go terrestris L., R. esczrlenta L. and R. temporaria L. The number of the optic nerve nonmyelinated fibers of the toad BuJo rerrestris is 370,000 (Maturana, 1959). The optic nerve of R. escu/enta has 14,600 myelinated fibers. 260,COOt_ 27,000 nonmyelinated fibers (Nikrui, 1969). The R. remporaria optic nerve fibers are distributed as follows: 210,000 & lS.000 nonmyelinated fibers and 8700-14.000 myelinated fibers (Manteyfel and Dyachkova, 1970). The total number of the cat’s retinal ,ganglion. cells is 90.000 (Stone, 1965). This amount falls within the number of the cat’s optic nerve fibers (120,000 fibers, Bishop, Jeremy and Lance, 1953; 119,000 fibers.

931

Breusch and Arey, 1942; 64,000 fibers, Verhaart. 1963). As mentioned above. Manteyfel and Dyachkova (1970) believe that the number of optic nerve fibers correlates with the dimensions of the body of amphibians under study. R. ridibunda is the biggest species of anuran in our fauna. Individuals of this species reach the dimension of 90-17Omm and the weight of 300 g while those of R. temporaria do not exceed the dimension of 55-6Omm (Terentjev, 1950). Unfortunately none of the aforementioned authors presents data on the dimensions of the frog species under their particular study and, above all, on their retina dimensions. The detectable difference in the total numbers of ganglion cells and optic nerve fibers of various amphibian species seems to be due to the difference in dimensions of their body and eyes. Data on the quantity of the lake frog’s optic nerve fibers are not to be found in the literature. As mentioned earlier (Kalinina, 1974b), the first type ganglion cells are very similar in their characteristics to the first class neurons of Lettvin et al. (1961). The data on the frequency of occurrence of the cell types described by the author are also close to those for Lettvin’s neurons. The frequency of occurrence of the first type neurons according to the author’s classification among other neurons is 96.7% in the central retinal zone (Table 1). From the data of Lettvin er al. (1961) the nonmyelinated fibers of the first and second class detectors also amount to about 97% of the total number of the optic nerve fibers. According to the data of Maturana et al. (1960). small ganglion cells with a perikaryon diameter of 7-lO/tm make up the greater part of these, namely 96%. Some authors relate the first and second class neurons to one and the same population presenting as the evidence of their similarity the numerous properties of their receptive fields obtained in electrophysiological experiments (Keating and Gaze, 1970). Probably it is due to this that the author could not carry out a morphological classification for the extensive group of the first type neurons. If the receptive field dimensions of various classes of retinal detectors are determined mainly by the dimensions of the dendrite fields of a certain type (Brown and Major, 1966: Stepanov, Serov, Lenshina and Kalinina, 1967; Stepanov, Kalinina and Lenshina, 1970), the first morphological type neurons should function as the first and second class detectors possessing the smallest receptive fields and nonmyelinated axons (Lettvin et af., 1959; Maturana ef al., 1960). The first and second class detectors are known to specialize in the detection of small objects. The considerable decrease in density of the first morphological type ganglion cells in the retinal periphery may indicate a specialization of the frog’s central retinal zone in the discrimination of small objects. The rotatory motion of a frog before it jumps upon a prey (Pygarev, 1970; Ingle, 1971) is probably connected with the necessity to shift the image to the central retinal zone. The author failed to find differences in the morphological structure of the first type neurons pertinent to their dendrite ramifications. Yet there is a small difference in the shape of nuclei and of cell bodies of these neurons: some of them are spherical and others are ellipsoidal. At present there are no data on the correlation between the shape of cell bodies

and the specific function of the neuron. That is why the author assumes the detection properties of the neurons of the first and second classes to be to a greater extent determined by the interconnections in more distal nerve cells (photoreceptors, bipolars, horizontal celis and amactines) than by the structural properties of the ganglion cells themselves. The second type neurons, distributed more or less uniformly over all retinal zones, are comparatively scanty. As pointed out earlier (Kaiinina, 1974b), the cells of this kind were not found in other species of the frog. At the same time R. ridibwnda was found to have the same classes of detectors as R. rempornria, R. pipiens and R. esculentn. This species of frog was not found to have any detectors different from those described earlier. The author believes that the second type neurons may be the so-called nonspecialized gangiionic cells whose axons in the amphibian do not go into tectum opticum but into the phylogenetically younger formations of the brain, i.e. into the thalamus nuclei (Munz. 1962, 1964: Knapp, Scalia and Riss, 1965: Karamyan, Zagoroolko, Belekhova and Veselkin, 1966: Pygarev and Zenkin, 1969). It would be interesting to evaluate the sum of dendrite field areas for neurons of various types per retinal area unit. Table 2 shows average values of Table 2. Average number of neurons of various types (11-V) revaluated for 1 mm’ of the retina

Tabic 3. Sums of dendrite Geld areas for neurons of the second. third. fourth and fifth types

neuron quantities for four types evaluated for 1 mm2

of the retina of the three zones studied. and the average quantity of cells of these types for the retina as a whole. There are no data on the receptive fields of the first type neurons in Table 2 for they are not determined (Kalinina. 1974b). The average areas of the dendrite fields are: O.~l~~, 0.006753, 0.018711 and 0.085036 mm’ for the second, third. fourth and fifth neuron types, respectively (Kalinina. 197413).The correlation of areas for neurons of the second, third, fourth and fifth types is presented in Fig. 2. Multiplying the average dendrite field area b> the average number of neurons of a certain type per 1 mm1 of the retina. the sums of neuron dendrire field areas for each of the four types over the area of 1 mm’ were found (Table 3). It can be seen that the retinal surface is most densely covered with the dendrite fields of rhe third type neurons. up to 99%. The dendrite fields of the second type neurons cover only 147; of the retinal area. The figures found for the fourth and fifth types are even smaller. For neurons of the various types a certain site of the retina occupied by these neurons and determined b) their dendrite field is typicai. The ensemble of the dendrite fields of each of the neuron types makes up an original pattern on the retinal surface. If the arrangement of the dendrite fields of the second, third ----.-....__

Fig. 2. Neurons of the second, third. fouith and fifth types. Impregnation with silver br the Gross-Bilshovsky-Lavrentyev-Feldmann method. Total retina. Drawing Oil immersion objecbve 90, eyepiece 10. Dendrite fields are outlined b> dotted lines. a-axon.

Quantity and topography of frog’s retinal ganglion cells and fifth types may be called mosaic, those of the

fourth type neurons are arranged in concentric rows round the blind spot in a chess like pattern. The dendrite fields of neurons of one and the same type do not usuaHy overlap except the rare cases of one-typeneurons forming a group of 2-3 cells. REFEREX3.S

Abercrombie M. (1916) Estimation of nuclear population from microtome sections. ,-ttnar. Rec. 94. 239-247. Bishop P. 0.. Jeremy 0. and Lance J. W. (1953) The optic nerve, properties of a central tract. J. Phpiol.. Lo&. 121. 415332. Blinkov S. M. and Gleser I. I. (1964) Brain of Jfan in Figures and Tables. IMeditsina. Leningrad, Breusch S. R. and Arey L. B. (19-12)The number of myelinated and unmyelinated fibers in the optic nerve of vertebrates. J. camp. ?ieurol. 77, 631-656. Brown J. E. and Major Diane (1966) Cat retinal ganglion cell dendritic fields. Expl Netrrol. 15, 7C&78. Cajal y Ramon S. (1893) La retine des vertebres. Cell& 9. 119-225. Cajai y Ramon S. I i909-191 ii ~isto~ogie da Spteme Xerretfx de i’Homme et des Verrebr& Tome II. Maloine, Paris. Chievitz J. H. (18S9) Untersuchungen iiber die Area centralis retinae. &ch. Anat. Physiol., Lpz.. Anat. Abtheil., Suppl. 139-396. Feldmann N. G. (1939) Methods of ontogenetic investigation of visual apparatus. .4rklt. biol. Nauk. $3. 154-157. Ingle J. 0. (1971) Discrimination of age orientation by frogs. Vision Res. 11. 1365-1367. Jacobson M. (1962) The representation of the retina on the optic rectum of the frog. Correlation between retinotsctal magnification factor and retinal ganglion cell count. Q. J1 e.rp. PhJsiol. 47. 170-178. Kalinina A. V. (1969) Binuclear cells of frog’s retina. V Volga Regional Conference of physiologists, biochemists and pharmacologists with morphotologists taking part, pp. 491-492. Mater.. Jaroslavl. Kalinina A. V. (19701 Classification of neurones of the retina by their quantitative characteristics. IX Inn Congr, of .&atom&s, Leningrad, 17-22 August 1970, p. 233. Trr. dokl., Moscow. Kalinina A. V. (197-tal On binuclear cells of the ganglionic laver of the frog retina. Arkh. anat. 67. 54-59. Kalinina A. V. (1973b) Classification of frog retina neurons by their quantitative characteristics. Msion Res. 14. 1305-1316. Karamyan A. I.. Zagoroolko T. M., Belekhova M. T. and Veselkin N. P. (1966) Evolution of visual system of inferior vertebrais. Sb. Mekhanismy kodirovanya trytelnoy Infbrmars~_~ pp. 49-66. Nauka ;Moscow. Kentin M. J. and Gaze R. M. (1970) Observations of the “surround” properties of the receptive fields of frog retinal ganghon‘cells. Q. J1 exp. phvsiol. 55. 129-141: Knaoo H.. Scalia F. and Riss W. (196% The oatic tracts of’&ta pipiens. .acra neural. wand. 4i, 325-355. Lashley K. S. (1932) The mechanism of vision. V. The structure and image forming power of the rat’s eye. J. camp. Pr~chol. 13. 173-200. Lettvin J. Y.. Maturana H. R.. hlcCulloch W. S. and Pitts W. H. (1959) What the frog’s eye tells the frog’s brain. Proc. inst. Radio Engrs 47. 1910-1951. Lettvin J. Y.. Maturana H. R.. Pitts W. H. and McCuIloch W. S. (1961) Two remarks on the visual svstem of the frog. In Sensory Commtmicarion (Edited b; Rosenblith W.). pp. 757-776. Wiley, New York.

Y.R. Ifin’)---0

933

Manteyfel Yu. B. and Dyachkova L. N. (1970) Ultrastructure and functional characteristic of visual nerve of Rana temporaria L. at normality and degeneration levels. .~e~rop~~sioloy~i~~ 2. 627-631. Maturana H. R. (19391 Number of tibres in the optic nerve and the number of ganglion cells in the retina of anurans. .l’artrre. Lond. 183. l-106-1407. Maturana H. R.. Lcttvin I. G., Pitts W. H. and McCulloch W. S. (1960) Physiology and anatomy of vision in the frog. J. gen. Physiol. 43. l29-175. Muntz W. R. A. lI962) Micro-electrode recordings from the diencephalon of the frog (Rana pipiensl and a bluesensitive system. J. :Veuroph_rsiol.25. 699-7 11. Muntz W. R. A. (1964) Vision in frogs. Scient. Am. 210. 110-119. Nikrui ?I. (1969) Fibers sizes and frequencies in the optic nerve of Raua escctlenta. Z. mikr.-anar. Forsch. 80. ~5O-J56.

Oehme H. (1961) Vergleichend-histologische Untersuchungen an der Retina van Eden. Zool. Jb. Anar. 79. 439-478. Pygarev I. N. (1970) Role of retinal detector system of the vertebral in visual information transmission, Dissertation for biology degree. iMoscow. Pygarev I. N. and Zenkin G. M. (1969) Evolution of visuaf anaiyser and development of two visual information channels. Zh. erol. byokhim. PIiysiol. 5. 419422. Shibkova S. A. (1970) Ganglion cells of the frog retina. Archs Anat. Hisrol. Embryol. 59. 72-77. Shkolnik-Yarros E. G. (1971) Asymmetrical dendritic fields of ganglion celis of the retina. !v’europhysioiogy 3. 301-307. Shkolnik-Yarros E. G., Podugolnikova T. A. and Dyubina A. P. (1975) Microscopic studies of the comparative morphology of the retina. ~Veuroph~sio~og~7. 66-73. Stepanov A. S.. Serov N. P., Lenshina L. K. and Kalinina A. V. (1967) Simulation of eye nervous network, pp. 37S-393. Scientific Report. Applied Mathematics and Cybernetics, Lobachevsky State University. Gorky. U.S.S.R. Stepanov A. S.. Kalinina A. V. and Lenshina L. K. (1970) Some structural functional features of nerve net of ganglionic cell receptive held. IX Congr. of the All-Union Parlot Physiology Sot., p. 161. Tez. dokl.. Leningrad. 1970. 2. Nauka. Leningrad. Stone J. (1965) A quantitative analysis of the distribution of ganglion cells in the cat’s retina. J. camp. .Yercrol. 124, 337-352.

Terentjev P. V. (1950) The Frog. Sovetskaja Nauka, Moscow. Urbakh V. Yu. (1963) .~~~r~ef~arica~Statisricsfor Biologisrs and Physicians. .\N SSSR, Moscow. Van Burren J. M. (1963) The Retinal Ganglion Cell Layer. Charles C. Thomas. Sorinefield. Ill. Van Crevel H. and Verhaary W. J. C. (1963) The rate of secondary degeneration in the nervous system. II. The optic nerve of the cat. J. Anat. 97. 451-46-1. Venslauskas M. I. and Gutauskas A. I. (1972) Analysis of the distribution of the orientation angles of the dendrites of amacrine and ganglion cells of the retina. ilrkh. anat. 63. 6168.

Venslauskas M. I. and Gutauskas .4. I. (1973) Geometry of dendritic tree of the retinal ganglionic cells. .Veurophp siologx 5. 307-314.

Vilter V. 0. (19499)Recherches biometriques sur l’organisation synaptique de la retine humaine. Sot. Bioi. 143. 11-12. Weymouth F. E. (1953) Visual sensory units and the minimum angle of resolution. Am. J. Ophthal. 46. 102-113.

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